This invention relates generally to cellular telephones and more particularly to a phone annunciation and battery measurement system.
Cellular telephones are typically used when an operator is performing other duties, such as driving a car. However, conducting various phone operations, such as dialing, require the phone operator to remember and select a long sequence of number on the phone keypad. Thus, the phone operator is distracted from other activities while dialing the phone number.
Cellular phones also annunciate different conditions to the phone operator. For example, a light emitting diode (LED) is activated when the phone battery is below a given charge level. These annunciators use additional space on the phone and add additional mechanical components which increase manufacturing costs.
The phone battery must be monitored to ensure successful message communication. For example, a phone conversation may be unintentionally cut short if the phone battery does not have sufficient charge. If notified early enough, the phone battery can be recharged or replaced before the phone becomes inoperable.
Digital Cellular telephones transmit and receive digital messages during various time slots. During the data transmit time slot, the phone's power amplifier (PA) is temporarily activated creating a large current drain in the battery. After the phone transmission is completed, the current drain on the battery is reduced.
Because the battery load continuously fluctuates, battery charge is difficult to measure accurately. If the battery supply voltage is measured during a high load condition, for example, during a voice transmission, the battery will appear to have a low charge. However, if measured during a low load condition, for example, before or after a message transmission or reception, the battery supply may appear to have a high charge. Thus, simply measuring the phone battery periodically does not accurately determine the remaining charge in a power supply used in a cellular phone.
Accordingly, a need remains for annunciating cellular phone conditions and initiating corresponding phone operations in a more efficient and cost effective manner while more accurately measuring charge in a cellular phone battery.